We are interested in the structure, regulation and in vivo function of myosins in nonmuscle cells. Our approach is to use anatomical, biochemical, cell biological and genetic methods to study the two distinct forms of nonmuscle myosin, myosin I and myosin II. We have cloned several different genes encoding the heavy chain subunits of both myosin II (a nonmuscle myosin possessing conventional structure) and myosin I (a low molecular weight, monomeric, nonfilamentous nonmuscle myosin). Current efforts are directed at: (1) determining the in vivo function of myosin I by examining the phenotype of myosin I-deficient cells generated by genetic means, (2) structure/function analysis of the unconventional C-terminal domain of myosin I (both protozoan myosin I and a vertebrate form of myosin I, the intestinal brush border 110 kDa protein), (3) full characterization of a third type of nonmuscle myosin distinct from myosin I and myosin II, and (4) testing models of myosin II filament formation and enzymatic regulation using site-directed mutagenesis and expression in E. coli. These basic studies shed light on the molecular basis of actomyosin-linked cellular motility, which in turn may increase our understanding of many cellular processes crucial to clinical medicine, such as white blood cell chemotaxis, cancer cell migration, angiogenesis, and wound healing.